There are a number of invasive plant species living and growing in the Municipal District of Bonnyville. Through a feature on our Facebook page, we are helping spread the word about these species. This page will be updated a couple of times a month to coincide with the Facebook posts #WeedWednesday.
The information on this page has been provided by the Alberta Invasive Species Council, unless otherwise noted.
Perennial Sow Thistle (Sonchus arvensis)
Perennial sow thistle has long been an aggressive agricultural weed, but can invade both natural and disturbed sites. It is a perennial plant that reproduces both by seed and creeping roots (rhizomes). Above ground portions of mature plants die in winter and new shoots sprout from root buds in spring. Many native lettuces closely resemble perennial sow-thistle, but they either do not have the extensive root system or their flowers are a different color. Annual sow thistle is very similar but reproduces only by seed and its flowers are smaller. Native to western Asia and Europe and was probably introduced as a seed contaminant.
Stems: Stems are upright, leafy at the base, branched in the tops and grow up to two metres tall. Cut stems exude a milky juice. Leaves: Leaves are alternate and waxy, with weakly prickled edges and the shape is variable. Lower leaves are stalked, but clasp the stem higher up. Leaf color varies from light to dark green and they can be up to 20cm long. Flowers: Flowers are small, yellow and dandelion-like. They are grouped in loose clusters at the ends of stems. The bracts of the flower heads are often covered with sticky hairs. One plant may have up to 20 flower heads, but with only few in bloom at a time. Flowers have both male & female organs but are generally self-incompatible, and are pollinated by insects. Seeds: Seeds are tufted to aid in wind dispersal. Seeds can germinate in spring or fall – fall seedlings overwinter as rosettes. Seed production is highly variable and seeds are relatively short-lived.
New infestations must be controlled before the extensive root system develops.
Grazing: Perennial sow-thistle is not especially palatable to livestock. Invasive plants should never be considered as forage.
Cultivation: Seedlings are easily controlled by cultivation. Intense cultivation over long periods can exhaust root reserves of mature plants, but root pieces as small as 1 cm can produce new plants.
Mechanical: Mowing can prevent seed production, but the plant’s long flowering period would necessitate many cuts. Seedlings can be easily hand-pulled.
Chemical: 2,4-D, Aminopyralid, Bromoxynil, Clopyralid, Chlorsulfuron, Dicamba, Dichlorprop in a product mix with 2,4-D, Florasulam, Glyphosate, Glufosinate ammonium, MCPA, MCPB and Quinchlorac are registered for use on perennial sow-thistle. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman or Certified Pesticide Dispenser for more information.
Biological: The possibilities of using the natural enemies of S. arvensis for biological control have been studied (Schroeder, 1973). Introductions were made into Canada, starting in 1979. Tephrititis dilacerata did not become established despite an extensive release program. Cystiphora sonchi is established but suffers heavy parasitism and is not effective. Liriomyza sonchi was established in Nova Scotia in 1987 and was under evaluation in 1990 (Julien, 1992).
Yellow Toadflax (Linaria Vulgaris)
Yellow clematis is a perennial vine of the buttercup family, native to high mountain areas of China and India. It reproduces both by seed and vegetatively from stem pieces. Vines grow rapidly either along the ground or will climb and cover other shrubs/trees, fences and trellises. It is widely available as both an ornamental plant and seed under a variety of names - Golden Clematis, Golden Tiara, Virgins-Bower - from seed; Radar Love, Helios. C. tibetana is a very similar yellow flowered clematis that is also available and hybridizes with C. tangutica. Yellow clematis has become very common and becoming abundant at some sites in the Bow Valley corridor from Wheatland County through Calgary to Canmore; also in city of Medicine Hat, town of Jasper, city of Edmonton, MD of Pincher Creek2 . In Alberta there is a native blue-flowered clematis which grows in the foothills – C. occidentalis or common names Blue clematis, blue Virgin’s Bower . A white-flowered clematis native to western N. America is C. ligusticifolia var. ligusticifolia – Western white clematis or white Virgin’s Bower.
Stems: Several stems per plant, growing up to 3-4 m long. Young stems are green while the older stems are tough & woody.
Leaves: Are bright green and compound with 5-7 lance-shaped leaflets 5-6 cm long, which may be lobed. Leaf tips are pointed and leaf edges are coarsely toothed. Leaves may be slightly hairy on the underside and are deciduous.
Flowers: Are lemon-yellow, nodding, with four petals, and appear mid-summer through late fall. Flowers are bell-shaped at first and then flatten as the petals spread. Petals may be silky-hairy on the outside and occasionally tinged purplish-brown. Flowers are borne at the ends of stems or in leaf axils – usually solitary but sometimes 2 or 3 together -on a short (0.5-3 cm) peduncle1 (flower stem). Bracts are similar to the leaves but smaller. Seeds are oval (3.5-4.5 mm long) with silky tails about 5-6 cm long.
Yellow clematis is distributed mainly through the nursery trade, and then spreads far beyond the gardens and flowerbeds via its abundant, wind dispersed seed. Do not purchase plants or seeds labeled with any of the names listed above.
Grazing: Not known. Invasive plants should never be considered as forage.
Cultivation: Not known. Unlikely since stem pieces can produce new plants and vines climb and out-shade any competing vegetation.
Mechanical: Repeated hand pulling prior to seed set can provide effective control and possibly eradicate small infestations.
Chemical: Currently no herbicides are registered for use on yellow clematis. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman or Certified Pesticide Dispenser for more information.
Biological: None researched to date.
Yellow Toadflax (Linaria Vulgaris)
Brought from Europe over 100 years ago as an ornamental plant, Common toadflax has escaped and has now become a serious problem to rangeland and mountain meadows all over North America. This perennial plant makes seed, but reproduction is primarily by sprouting from its extensive, creeping root system (rhizomes) – 2-3 week old seedlings can produce creeping roots. The ability of this plant to form large colonies allows it to crowd out other vegetation. Common toadflax is easily confused with Leafy spurge before flowering, but toadflax stems do not contain the milky latex that spurge does.
Stems: Stems are erect, hairless, generally un-branched and can be as short as 15cm or grow to 1 m tall. Mature plants may have 1 to 25 stems.
Leaves: Leaves are soft, lance-shaped, pale green, and very numerous. Leaves are mainly alternate but may appear opposite on the lower stem due to crowding. Leaves can be up to 10 cm long and are attached directly to the stem. The most distinctive difference between Yellow and Dalmatian toadflax is that Dalmatian toadflax has broad, heartshaped leaves that clasp a woody stem; whereas, yellow toadflax has narrow, linear leaves with a narrow stem1 .
Flowers: Flowers are bright yellow, arranged alternately in dense spikes at the ends of stems and have a long spur extending from the base that is usually as long as the flower itself – in all, 2 to 3.5 cm long. The snapdragon-like flowers can have orange colouring on the throat. They flower at different times depending on site conditions. In high elevations they could flower as late as July. Flowers are identical to Dalmatian toadflax, but leaf shape differs between the two plants.
Seeds: The seeds are winged, disk-shaped, and dark brown to black. Despite its prolific seed production (5000 seeds/stem) and long viability (up to 10 years), germination rates are often very low – less than 10%.
Spurred snapdragon, another common name for this plant, often appears in wildflower seed mixes. Do not purchase seed mixes unless all contents are listed.
Once present, it establishes dense patches that are extremely difficult to control, let alone eradicate. Multiple control methods and several years of commitment provide the best success.
Grazing: Pasture invasions flourish because the plant is not palatable to livestock.
Cultivation: Repeated cultivation can effectively destroy the root system. Equipment should be thoroughly cleaned after.
Mechanical: Thorough hand-pulling can be effective in soft soils where the roots can be removed easily. Repetition is required to deplete the seed bank and all root pieces. Mowing can assist by starving the roots.
Chemical: Acetic acid, Amitrole, Dichlorprop, Diuron, Glyphosate, Hexazinone, Imazapyr, MCPA, Metsulfuron-methyl, Picloram and Tribenuron-methyl & Thifensulfuron-methyl (in a product mix) are registered for use on toadflax. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman or Certified Pesticide Dispenser for more information.
Biological: Several biological control agents have been imported to control Common toadflax. New Alberta research shows a stem mining weevil, Mecinus janthinus, successfully established and providing effective control.
Meadow Hawkweed (Hieracium caespitosum)
Meadow Hawkweed has not been found in the MD of bonnyville to date but this is one to keep your eye out for. It is hard to distinguish this one from other yellow weeds but if you take a read thought the Alberta invasive species fact sheet should make a bit easy to ID.
Meadow hawkweed is a member of the Aster Family native to Europe. It is a fibrous rooted, perennial herb with a milky latex in the stems and leaves. Hawkweeds reproduce by seeds and vegetatively by numerous horizontal stolons, and rhizomes underground. Seeds are produced by apomixis - asexually - as nonnative hawkweeds are polyploids, as opposed to the native diploid hawkweeds. Occasional sexual reproduction occurs. Hawkweeds develop a low rosette of basal leaves before producing a flowering stem. Dandelion-like flowers are borne at the ends of stems. Non-native hawkweeds exhibit many characteristics of an invasive plant: high seed production and germination rates, asexual seed production, wind-dispersed seed, vegetative reproduction via rhizomes, stolons, and root fragments, and rapid growth. A few invasive hawkweed species are popular ornamentals. All of these characteristics facilitate rapid colonization and monopolizing of resources. An undetected patch of hawkweed has great potential to become an uneradicable infestation.
Stems: Are erect, solitary, and bear simple, glandular and stellate hairs.2 Plants grow 20-70 cm.1 Stolons are sometimes short and inconspicuous.
Leaves: Basal leaves are oblong/lance shaped to spoon-shaped, and 5-25 cm long 1-3 cm wide. Basal leaves are persistent and have petioles. The upper leaf surfaces bear long simple hairs and few to none stellate hairs. The lower surfaces bear moderately dense stellate and long simple hairs. Leaf margins may be entire or minutely toothed.
Flowers: Yellow ray flowers are borne in compact, flat-topped clusters of 20-50.1 Involucral bracts are lance-shaped, 5-9 mm tall, not graduated, and bear many simple and glandular hairs, and a few stellate hairs. Achenes are 1.5-2 mm long, with a dirty white pappus.
Learning to recognize hawkweeds from the many yellow-flowered members of the Aster Family is key to prevention. Hairs are an important characteristic of non-native hawkweeds and also in distinguishing between species. Stolons facilitate rapid colonization of a patch of ground. Long term management of hawkweeds requires maintaining healthy forbs and grasses - fertilization of desirable vegetation can result in out-competition of hawkweeds. Re-seed disturbance in areas susceptible to hawkweed invasion.
Grazing: Unknown. Invasive plants should never be considered as forage.
Mechanical: Mowing before flowering will prevent seed production of taller plants but will not inhibit reproduction via stolons and rhizomes. Hand digging of small infestations where all stolons and root can be removed may be effective. Root fragments can generate new plants, therefore any mechanical tilling/cultivation would be ineffective.
Chemical: Hexazinone, 2,4-D, and glyphosate are registered for use on Hieracium spp./hawkweeds. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Consult your local Agricultural Fieldman or Certified Pesticide Dispenser for more information.
Biological: None researched to date.
Common tansy is a perennial forb that reproduces by both seed and short rhizomes (underground horizontal roots). Introduced from Europe in the 1600’s, its pungently aromatic foliage has been used medicinally, as an insect repellant, and for embalming.
Common tansy forms dense stands and the plants contain alkaloids that are toxic to both humans and livestock if consumed in large quantities. Cases of livestock poisoning are rare, though, because tansy is unpalatable to grazing animals.
Stems: Stems are branched, erect, often purplish-red, and dotted with glands. There are many stems per plant and grow up to 1.5 m tall.
Leaves: Leaves alternate on the stem and are deeply divided into numerous narrow, individual leaflets with toothed edges.
Flowers: Flowers are yellow, numerous, and button-like, occurring in dense, flattopped clusters at the tops of the stems.
Seeds: Seeds are yellowish brown achenes with short, five-toothed crowns.
Because of its long medicinal and horticultural use, Common tansy is still available in plant nurseries and from herbal remedy suppliers. Gardeners should not purchase or grow Common tansy
Grazing: Common tansy is unpalatable to cattle and horses, but sheep and goats are reported to graze on it.
Cultivation: Since this plant is rhizomatous, flowering stems can re-grow from severed roots, therefore cultivation is not a control option.
Mechanical: Regular mowing can reduce seed production but must be repeated to eliminate regrowth from rootstock. The most effective control method combines mowing or hand cutting with chemical control and encouraging competition from native vegetation. Repeated stem removal depletes the food energy stored in roots.
Canada Thistle (Cirsium arvense)
A colony-forming, aggressive perennial, that spreads primarily by its creeping root system. Despite its name, the plant was introduced from Europe, and is the only thistle, native or introduced, with separate male & female plants. Also called “Creeping Thistle,” the roots spread both horizontally (up to 4.5 metres) and vertically (up to 6 metres) underground. It has been estimated that individual plants live about 2 years, but are continually replaced by new shoots from adventitious buds on its extensive root system. This can result in infestations composed entirely of genetically identical plants of one sex. Dense riparian infestations can impact wildlife by reducing food, and access & nesting cover for waterfowl.
Stems: Stems are grooved, upright, hollow and woody, branching near the top, and grow .5 m to 1.5 m tall.
Leaves: Leaves are lance-shaped, dark green, shiny on the surface and occur alternately, slightly clasping the stem. Lower leaves are largest and decrease in size upward along the stems. Leaf edges can vary from smooth with no spines to irregularly lobed with sharp spines.
Flowers: Flowers form at the ends of stems in clusters of one to several. The flower head is urn-shaped and the bracts are spineless. The colour of the flowers may vary from plant to plant, being purple, pink or white.
Seed: Seeds are borne in an achene 2 to 4 mm long which is tufted to aid in wind dispersal. Most seeds germinate within a year, but buried seed can stay dormant for up to 20 years.
The best preventive measure in non-cropland is to maintain healthy plant cover and to reseed disturbed areas with a desirable species as soon as possible. Canada thistle seedlings are very shade intolerant and will not establish under low light conditions. Avoid overgrazing to prevent thistle establishment in pastures/rangeland.
Most of the biomass of Canada thistle plants is below ground; therefore killing the roots is the only effective control method. An integrated management plan that uses a variety control options is the most effective long term strategy for reducing infestations. Grazing: Sheep and goats will readily graze thistle, but not so much in the spiny stage. Occasionally livestock will randomly graze thistle, even when other forage is available, however removal of the stems by grazing only stimulates re-sprouting by the plant. Invasive plants should never be considered as forage.
Cultivation: Cultivation only produces small root pieces that rapidly develop into new plants, and does not reach the deeper roots.
Mechanical: Repeated mowing through the growing season gradually depletes the food energy stored in the root system. Repeated hand pulling in loose soils can also effectively stress the root system. To succeed, several years of effort must be committed.
Chemical: 2,4-D, Aminopyralid, Chlorsulfuron, Clopyralid, Dicamba, Glyphosate Hexazinone, Metsulfuronmethyl, MCPA and Picloram are some of the herbicides registered for use on Canada thistle. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman or Certified Pesticide Dispenser for more information.
Biological: Several weevils and one fly have been imported to target Canada and other thistle species, but a few are no longer recommended due to impacts on native thistle species
Himalayan balsam (Impatiens glandulifera)
Himalayan balsam is a summer annual of riparian areas which reproduces by seed only.
Native to the western Himalayas, it was introduced to Kew Gardens in the early 1800s. By the 1900s it was already common in southwest Germany and spreading via the Rhine River, and throughout Scandinavian countries by the mid-1900s. Today it is widely known as an invasive alien in temperate areas of Europe, Asia, North America and New Zealand. In Alberta, there are patches along water courses within the cites of Edmonton and Red Deer, as well as Parkland County.
Seeds germinate in the spring to produce dense, even-aged stands which shade-out competing vegetation. It then exhibits an impressive growth rate for an annual with some plants growing to three metres tall.
Himalayan balsam has a shallow, fibrous root system but adventitious roots from the lower stems provide some buttressing. However in winter, erosion can occur as a result of balsam’s shallow rooting having replaced the deeper rooted native vegetation.
Plants flower from July until frost. Flowers are self-compatible but the anthers release their pollen before the stigma is receptive, therefore plant requires pollinators. Himalayan balsam attracts pollinators away from native species with its high nectar content and extended flowering. It is a late season nectar source for butterflies, bees and bumble bees.
Mature seed capsules explode when disturbed and eject the seeds, hence another common name of Touch-Me-Not plant. Medium sized plants produce on average 700 to 800 seeds which can be flung as far as five metres from the parent plant. Seeds do not float, but can be carried along in water currents and can germinate under water and when fully soaked – seed viability is about two years.
Stems: Are smooth, hairless, and usually hollow, tinged red-purple and are easily broken. Stems grow one to three metres tall and there may be some branching.
Leaves: Are lance shaped or elliptic with pointed tips and rounded bases, and six to 15cm long. The leaves are stalked and have sharply serrated edges. They occur opposite or in whorls of three. Leaf size decreases with height on the stem.
Flowers: Are large – two and a half to four cm long – in shades of pink through purple, occasionally white. Flowers occur five to 10 together in racemes on long stems borne in the upper leaf axils. Flowers have five petals and are bilaterally symmetrical. The upper petal forms a hood over the reproductive structures (resembling a British policeman’s helmet) and the lower petals form a platform for landing. Seed capsules are one and a half to three and a half cm long and up to one and a half cm wide and contain up to 16 seeds which are four to seven mm long and two to four mm wide. Seeds require cold stratification before germination.
Initial spread is mainly from ornamental plantings – do not purchase or grow Himalayan balsam. Seed can be spread by movement of riparian soil and in the sediment from the bottoms of water courses of infested areas. Remedy soil disturbance in suitable habitats. Any control work on infested stands must be done before flowering.
Grazing: Sheep and cattle have been known to graze the plant in Britain without ill effects. Invasive plants should never be considered as forage.
Cultivation: Likely very effective but cultivation is not practical in riparian habitats.
Mechanical: Mowing can be very effective but may need to be repeated as cut plants can grow new flowering branches, and would be difficult in riparian areas. Himalayan balsam plants are easily hand pulled due to the shallow root system. Plant debris should be incinerated or bagged and sent to the landfill.
Chemical: Currently no selective herbicides are registered for use on Himalayan Balsam. The use of herbicides in aquatic environments requires Alberta-specific applicator certification and permits. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman (780-826-3951) or Certified Pesticide Dispenser for more information.
Biological: CABI began researching natural enemies in 2006 and host specificity testing began 2008.
White Cockle (Lychnis alba syn. Silene alba S. latifolia)
White cockle was introduced from Eurasia and is often confused with bladder campion (not hairy, not sticky) or night-flowering catchfly (hairy, upper stems sticky), white cockle is not sticky on any part of the plant. It is a short-lived perennial (sometimes biennial) native to Europe. Plants are either male or female, so not all plants produce seed.
Stems: Stems are hairy, grow 30 to 120cm tall, and can be erect or spread laterally. There can be several stems per plant – crowded plants branch in the upper stems. Stems are swollen at the nodes.
Leaves: Leaves are opposite, hairy, and lance or slightly oval-shaped with pointed tips. Basal leaves and upper stem leaves are smaller.
Flowers: Flowers are numerous, fragrant and arranged in spreading clusters. The white (or pinkish) flowers have 5 notched petals and only open in the evening. The tubular calyx surrounds the flower’s base. The calyx of the male flower has 10 veins, and the female’s 20 veins are longer, and inflate with ripening.
Seeds: The calyx matures into a fruit with 10 teeth at the tip containing many tiny, grayish seeds.
White cockle seeds are similar in size to clover and so is often a contaminant of forage seed.
White cockle can be a serious economic problem as its seeds are difficult to separate from alfalfa, clover and some grass crop seeds – and this invader is an extremely heavy seed producer. This plant emerges early spring, initially forms a taproot, and next spreading lateral roots.
Grazing: Not grazed. Invasive plants should never be considered as forage.
Cultivation: Stem and root pieces can sprout to form new plants; therefore cultivation will usually spread an infestation.
Mechanical: Frequent mowing will reduce seed production.
Chemical: Mecoprop (in a product mix with 2,4-D and Dicamba) and Tribenuron-methyl (alone or in a product mix with Metsulfuronmethyl and quinchlorac) are registered for use on white cockle. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman or Certified Pesticide Dispenser for more information.
Biological: None researched to date.
Oxeye Daisy (leucanthemum vulgare)
Stems: Grow up to one metre tall and are smooth, frequently grooved and sometimes branch near the top (although more frequently unbranched).
Leaves: Progressively decrease in size upward on the stem. Basal and lower leaves are lance-shaped with “toothed” margins and petioles that may be as long as the leaves. The upper leaves are alternately arranged, narrow and often clasp the stem with wavy margins.
Flowers: Are borne singly at the end of stems and can be up to five centimetres in diameter, with yellow centres, and 20 to 30 white petals radiating from the centre. The petals are slightly notched at the tip.
The availability of closely related plants through the nursery and seed trade contradicts the perception of Oxeye as an invasive plant, and subsequent control. Shasta daisy is a cultivar (originated from) of Oxeye sold through nurseries and as seed in wildflower mixes. This fact makes public awareness critical to prevention and control. The two plants can cross breed, resulting in an invasive hybrid that is extremely difficult to distinguish from either parent. Invasive ornamentals can be very difficult to contain and should be avoided. Consumers should carefully read the contents of so-called ‘wildflower’ seed mixes and avoid those containing invasive ornamentals.
Grazing: Oxeye Daisy is avoided by cattle and therefore capable of dominating pastures and rangeland. Horses, sheep and goats, however, will readily graze oxeye daisy and can be used in companion grazing situations to control oxeye daisy. Switching to higher stock densities and shorter grazing periods does encourage cattle to eat and trample more of the plant. Intensive grazing and trampling slightly reduces the number of seeds produced, and presumably injures younger rootstalks. Trampling also brings dormant seeds to the surface and removes the canopy cover so those seeds will germinate with mid-summer rain showers. In normal years, those seedlings will dry-out and die before becoming established, further reducing the number of seeds in the seed bank. It should be noted, however, that intensive grazing in wet summers may increase the number of successful seedlings. As many as 40% percent of the seeds consumed by cattle may remain viable after passing through the digestive tract, so care should be taken to avoid spreading the seeds when moving stock.
Mechanical: Repeated mowing prevents seed production, but also can stimulate re-sprouting of stems. Hand-pulling or digging before seed production is effective, but it is important to remove as much of the fibrous roots and rhizomes as possible. Ground disturbance while digging should be kept to a minimum. Hand removal will have to be continued for several years because seeds may remain viable in the soil for a long time. Because of its shallow root system, oxeye daisy is easily killed by intensive cultivation.
Chemical: Aminopyralid alone or in a product mix with Metsulfuron-methyl or 2,4-D is registered for use on oxeye daisy. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman or Certified Pesticide Dispenser for more information.
Biological: In 2008 a literature study was conducted to investigate European insect species that feed on oxeye daisy. Studies on ploidy analysis, to be conducted by CABI, and molecular analysis, to be conducted by USDA-ARS, are underway with field collected and commercially available Shasta daisy cultivars to determine the relationship with the target oxeye daisy and assist in host range understanding of potential biocontrol agents. An international consortium, including the Alberta Invasive Species Council, is funding research at CABI1.
Scentless Chamomile (Tripleurospermum perforatum)
Stems: Stems are erect to semi-erect, highly branched, may be reddish in color, and can grow up to 1 m tall. There can be a few to many stems per plant.
Leaves: Leaves are alternate and very finely divided into short segments (carrot-like) and odorless when crushed. Basal leaves disappear by flowering time.
Flowers: Flowers are composed of a yellow central disk surrounded by white petals. The flowers are borne singly at the end of stems and have numerous bracts, arranged in overlapping rows.
Seeds: Seeds are tiny (about 2 mm), ribbed and dark brown. Seeds develop and become viable quickly
Scentless Chamomile does not compete well with vigorous, healthy plant communities. Dispersal by weed seed contamination in crop/grass seed and livestock forage is common. It can be very difficult to eradicate in crop situations.
Grazing: Scentless chamomile is generally unpalatable to grazers and its seeds can survive digestion. Invasive plants should never be considered as forage.
Cultivation: Late fall and early spring tillage will control rosettes. Frequent, shallow tillage can help exhaust the seed bank by repeatedly destroying germinating seedlings. Equipment must be cleaned after.
Mechanical: Mowing can prevent seed production but plants will re-bloom below the cutting height. Hand-pulling can prevent spread into new areas and is effective on small infestations. Pulled plants should be burned or bagged and sent to the landfill. Burning infestations that have finished blooming can prevent seed spread.
Chemical: Aminopyralid (alone or in a product mix with 2,4-D or Metsulfuron-methyl), Chlorsulfuron, Clopyralid (alone or in a product mix with MCPA), Dicamba, Glufosinate ammonium, Hexazinone, Picloram, MCPA (in a product mix with Bromoxynil), Metsulfuron-methyl and Tribenuron-methyl (in a product mix with Thifensulfuron-methyl) are registered for use on scentless chamomile. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman or Certified Pesticide Dispenser for more information.
Biological: A seed-head feeding weevil, Omphalapion hookeri, and a gall midge, Rhopalomyia tripleurospermi, have been released in Alberta.